This invention relates to improvements in a vehicular generator equipped with a cooling fan.
In general, a generator for use in a vehicle has its rotor driven by an engine. Usually, the rotor is driven at approximately double the rotational speed of the engine through a pulley. Since a cooling fan is fixed to the rotor, it is similarly rotated at approximately double the rotational speed of the engine. As will be stated below, this has caused disadvantages attributed to the cooling fan.
A prior-art device of this type is shown in FIG. 1 and FIGS. 2A and 2B. Referring to the figures, numeral 1 designates a stator, and numeral 2 designates a rotor positioned axially along the inner surface of the stator 1 leaving a minute air gap therebetween. First and second cooling fans 31 and 32 are fixed to the rotor 2 and include blades 311 and 321, respectively. A front bracket 4 supports the rotor 2 through a bearing, and is provided with a plurality of ventilating holes 41 and 42. A rear bracket 5 supports the rotor 2 through a bearing along with the front bracket 4, and is provided with a plurality of ventilating holes 51 and 52.
In operation, when the generator is driven by an engine, not shown in FIG. 1, the rotor 2 is rotated. The first and second cooling fans 31 and 32 mounted on the rotor 2 cause cooling air to flow from the ventilating holes 41 to holes 42 and from the ventilating holes 51 to holes 52, respectively. Thus, a cooling operation is effected.
In the prior-art device constructed and operated as described above, the cooling fans are rotated in proportion to the rotational speed of the engine irrespective of the level of the internal temperature of the generator. A large quantity of cooling air is accordingly circulated in the generator even where the temperature of the interior of the generator is low during the period of a low electric load during which much cooling air is not required. Especially at medium and high revolution speeds of the engine, the device has the disadvantages of increased power losses due to unnecessarily high speeds of the cooling fans, lower efficiency of the generator and increased noise of the cooling fans.